Studies making use of isolated proteins, ranging from production of antibodies to biochemical characterization of enzymes and animal injection studies of secreted signaling factors, are critical to understand their biological roles. To facilitate such studies, we plan to implement a Protein Expression Core Facility (the PE core). The PE core will produce and characterize purified proteins for members of the DERC. Specifically, the core will provide the following services: (1) Bacterial protein expression of recombinant proteins in E. coli. In general, only proteins with simple architecture will be produced in this system. (2) Mammalian expression using a cellsorting method to quickly enrich the fraction of highly expressing cells. (3) Purification using standard affinity, ion exchange, and gel filtration chromatography techniques. (4) Characterization of purity, appropriate folding, and oligomerization state, using standard biochemical methods and mass spectrometry.